1. Field of the Invention
For specific applications such as heavy armored vehicles, high speed boats, transportable generating sets, the diesel engine market requires diesel engines with a very high power density. This means very high turbocharged engines with high b.m.e.p.(brake mean effective pressure). The present Invention brings a way to make such engines with low fuel consumption and low emissions.
2. Description of the Related Art
With given swept volume and revolution per minute, an increase of the engines output need bigger amount of air for combustion. This amount of air depends on the inlet pressure. But the increase is limited because the higher is the inlet pressure, the higher is the pressure at the end of the compression stroke and the higher is the combustion pressure. A high combustion pressure may cause mechanical stresses in most of the components of the engine like the crankshaft. In addition to that, a high combustion pressure reduces the oil film thickness of the bearings and the life span of the piston rings.
One solution for maintaining the combustion pressure at a limited high level consists of reducing the compression ratio of the engine. But a low compression ratio makes the starting difficult and sometimes impossible. This is why some low compression ratio engines have an additional external combustion chamber. That combustion chamber must be started before the engine in order to give energy to the turbocharger. The combustion chamber and the turbocharger work together in a loop around the engine. When the air given by the turbocharger reaches a sufficient pressure and temperature, the engine can be started. Thanks to such combustion chamber, some engines run at a bmep of 35 bars. But the control of the combustion chamber, the engine starting phase and the idle are very sophisticated. The combustion chamber must be "on" all the time and the fuel consumption of these engines is rather high. The present invention offers a better solution for getting an output increase with a low compression ratio.